Abstract
BackgroundThe cerebral cortex is permanently active during both awake and sleep states. This ongoing cortical activity has an impact on synaptic transmission and short-term plasticity. An activity pattern generated by the cortical network is a slow rhythmic activity that alternates up (active) and down (silent) states, a pattern occurring during slow wave sleep, anesthesia and even in vitro. Here we have studied 1) how network activity affects short term synaptic plasticity and, 2) how synaptic transmission varies in up versus down states.Methodology/Principal FindingsIntracellular recordings obtained from cortex in vitro and in vivo were used to record synaptic potentials, while presynaptic activation was achieved either with electrical or natural stimulation. Repetitive activation of layer 4 to layer 2/3 synaptic connections from ferret visual cortex slices displayed synaptic augmentation that was larger and longer lasting in active than in silent slices. Paired-pulse facilitation was also significantly larger in an active network and it persisted for longer intervals (up to 200 ms) than in silent slices. Intracortical synaptic potentials occurring during up states in vitro increased their amplitude while paired-pulse facilitation disappeared. Both intracortical and thalamocortical synaptic potentials were also significantly larger in up than in down states in the cat visual cortex in vivo. These enhanced synaptic potentials did not further facilitate when pairs of stimuli were given, thus paired-pulse facilitation during up states in vivo was virtually absent. Visually induced synaptic responses displayed larger amplitudes when occurring during up versus down states. This was further tested in rat barrel cortex, where a sensory activated synaptic potential was also larger in up states.Conclusions/SignificanceThese results imply that synaptic transmission in an active cortical network is more secure and efficient due to larger amplitude of synaptic potentials and lesser short term plasticity.
Highlights
The cortical network in situ is permanently active, its patterns of activity varying depending on the waking or sleep states [1,2,3]
Twenty-nine neurons recorded from ferret cortical slices are included in this study (22 regular spiking (RS); 5 chattering (CH) and 2 intrinsic bursting (IB)), 27 neurons from cat visual cortex in vivo (14 RS; 5 CH; 2 IB; 3 fast spiking (FS); plus 3 non classified) and 14 neurons from rat barrel cortex in vivo (12 RS; 1 CH; 1 IB)
The main results are: 1) Synaptic potentials show more paired pulsed facilitation and synaptic augmentation in active than in silent cortical networks and 2) Synaptic potentials occurring during up or activated states of the cortex increased their amplitude with respect to those occurring during down states
Summary
The cortical network in situ is permanently active, its patterns of activity varying depending on the waking or sleep states [1,2,3]. The cerebral cortex is permanently active during both awake and sleep states This ongoing cortical activity has an impact on synaptic transmission and short-term plasticity. Intracortical synaptic potentials occurring during up states in vitro increased their amplitude while paired-pulse facilitation disappeared Both intracortical and thalamocortical synaptic potentials were significantly larger in up than in down states in the cat visual cortex in vivo. Induced synaptic responses displayed larger amplitudes when occurring during up versus down states This was further tested in rat barrel cortex, where a sensory activated synaptic potential was larger in up states. These results imply that synaptic transmission in an active cortical network is more secure and efficient due to larger amplitude of synaptic potentials and lesser short term plasticity
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